In general, a swing device for an infant has being operated such that it is swung back and forth at a regular time and interval, allowing an infant to get comfortable sleep or to play it. Although in the past, such swing device had been manually swung by the protector of an infant, recently, in order to dispense with such trouble, it has being developed an automatic swing device, which is automatically swung using external power.
Such automatic swing device may be divided by the drive mechanism into an electric type in which a rotational shaft of a cradle or a swing is directly driven by a motor, and an electromagnetic type in which a cradle or a swing is swung using a repulsive force between a permanent magnet and an electromagnet.
The electric type swing device between them has a problem in that since it operates by a motor, operational noise is generated and power consumption is large.
On the other hand, the conventional electromagnetic swing device is configured such that a permanent magnet is arranged on a seat on which an infant will sit down, an electromagnet is arranged on both positions back and forth along a rotational direction of the seat, and polarity is selectively changed so that the seat is swung back and forth by the repulsive force between the permanent magnet and the electromagnet. That is, when the permanent magnet approaches the electromagnet, the polarity of the electromagnet is changed identically to that of the permanent magnet to thus create a repulsive force between the permanent magnet and the electromagnet so that the seat is in turn swung in opposite direction by the repulsive force.
In building the swing device, the time to magnetize the electromagnet is very important. That is, it is the decision for the time of supplying the electromagnet with power. To this end, in the past, the respective electromagnets had been selectively changed through detecting a rotational angle of a seat using a photo sensor.
However, such electromagnetic type swing device has the problems in that if the photo sensor detects wrong positions of the seat, the polarity of the electromagnet adjacent to the permanent magnet is changed reversely to that of the permanent magnet to cause a malfunction such as stopping the seat at that position, as well as the structure thereof is complex.
Therefore, there is a need for a swing device that has a circuit for generating a repulsive force, capable of creating driving force with a simple construction using a permanent magnet and an electromagnet. Such circuit should also serve as a sensor for detecting a position of a swinging object, for example, the photo sensor as set forth above, and prevent the malfunction to detect a wrong position of the swinging object.